Vania



April 12, 11927'. C. R. HANNA TELEPHONE RECEIVER Filed A1121. 28, 1924 WITNESSES: @5%

' ATTORNEY Patented Apr. lltlfh l,ti?..4,338

NY, A GORFORATION 0]? PENNEYL .LONE RECEIVER.

Application led August 2, 1924. Serial No. 734,604.

lily-invention relates to telephone receiver devices and particularly to telephone receivers having permanent magnets.

One object ot my invention is to produce o a telephone receiver device in `which 'full utilization is made otl the properties et steels which have high coercive torce.

ln the steel, of which the permanent mag net in the telephone receiver disclosed herein is made, the changes in magnetic iinluction, corresponding to the small charges in lim pressed magneto-motive torce, which are superposed upon the permanent magnctomotive torce, are accompanied hy greater losses than in steelsheretoil'ore used. Another object of this invention is to provide a struc ture in which said losses are largely avoided.

Another object ot my invention is to produce a telephone receiver having a minimum amountvol permanent-magnet steel therein.

Another object otmy invention is to produce a telephone receiver having' a path tor the variable magnetic llux, distinct from the source ot' the permanent fluir.

Anotherobject of my invention is to produce a telephone receiver ot minimum Weight.

Another object of my invention is to produce Va telephone receiver device capable oit greater eliiciency ot translation it vihratory currents into sound than the devices ot the prior art. y

Telephone receivers `ordinarily have a diaphragm mounted in ay container case, Within which are also placed a permanent magnet, `pole pieces, attached' thereto and adjacent the center oli" the diaphragm., clectromagnet coils upon the pole pieces, and connecting and terminal blocks Jfor the `attachment of lead Wires. lt is customary tor the permanent magnet to be made in a. horseshoe' shape from such material tool steel. "With this construction there is a great deal ot leakage flux and only a small portion ot the total flux otl the magnet passes through the pole pieces and the diaphragm. The present invention, by providing a short straight magnet, avoids this disadvantage.

In structures wherein the tluX variations produced by the changing` signal current are requiredto take place Within the body of the permanent magnet, these tlui; variations are smaller thanit they occurred in a magnetic circuit containing sott iron, only.

This results in smaller vibrations of the diaphragm.

also the large Weight ot the permanent magnets in the receivers as formerly built is objectionable, particularly when the telephone is one ot a pair to be Worn upon lthe head ot an operator.

Elly invention provides means whereby a very short, small and light magnet is made to 'tarnish snliicient magnetic tlux for the operatioi'i ot the telephone receiver. My in vention tnrther comprises means whereby the above-mentioned disadvantage of the permanent-magnet steel is avoided.

@ther objects and structural details of my invention willbe apparent from the following description, When read in connection With the accompanyingdrawing, wherein:

Fig. l is a perspective view of the permanent magnet and pole pieces in my invention,

nig. 2 is a perspective view ol an alternative construction.

liig. 3 is a view partly in section ot the magnetic circuit embodying my invention,

liig. l is a 'View in sectional elevation ot' an embodiment ot my invention, and

liig. 5 is a diagram showing curves used in the explanation of the invention.

l permanent magnet l ot' a material such as cobalt steel which has a high coercive force, has attached to its pole the pole pieces 2 and 3. The pole pieces 2 and 3 are ol' L- shape and the lower portions ol the Ls are turned toward each other underneath the permanent magnet l. The lower portions of the lfs are separated from the permanent magnet l by a spacci' et, of non-magnetic material, preferably insulation. rlhe pole pieces 2 and 3 do not quite meet below the spacer 4l, but leave an air-gap 5 between their ends.

fr diaphragm G, shown in Figs. 3 and l, is adjacent the upper ends of pole pieces 2 and 3. f

Three paths for magnetic flux are provided, One path comprises the permanent magnet l, the pole piece 2, the air-gap 5, and the pole piece 3, back to the permanent magnet l.

l second pat-h vtor magnetic 'flux comprises the permanent magnet l, the upper portion olE the pole piece 2, an air gap 7 between the pole piece and the diaphragm, the diaphragm 6, a second air-gap 8, the upper por 1 position the windings.

prises the pole piecej, the air gap 5 tion of the pole piece 3 and permane-nt mag net 1. A third path for magnetic flux comthe pole piece 3,'the airgap 8, the diaphragm G, the air-gap 7, and the pole piece 2.

ilhe'receiver is mounted in a case 9, shoivn in- Fig.' 4f. The diaphragm-G is held in place by the cover 11,`and the,v electromagnet coils 12' and 14 are positioned upon the pole pieces 2 and 3. Thepole pieces 2 and 8 and the spacer 4 are held in place by the fastening means 115` and 16` and the binding. posts 1T and 18 are provided for the attachment of the connector wires 19 and 20. The windings 12 .and lei-I may be Wound on fullsizedf ends of the pole` pieces as in Fig. 1. or the pole pieces may have shoulders, as in Fig. 2, to

Inthe .operation of my device, the diaphragm Gis attracted vby the permanent magnet flux from the magnet 1 passing through .the second of the above-described magnetic paths. Varying fiuX is induced in the third-mentioned magnetic circuit by the fluctuating currents in the coils 12 and .1a. p. This flux producedby the [iuctuating currents acts to increase or decrease the force acting uponl the diaphragm 6, thereby causing it to move and to produce sounds.

Because the permanent magnet 1 is short, the'leakage of the permanent magnetic flux is a minimum. The magnet 1 is made of a steel which has high coerciveforce., In; order to makeclear .how the selection of a steel of high Acoercive force results in the possibility of a short magnet, consider the change of the induction with alterations in the'impressed magnetizing force.V in the manufacture of the'zpermanent magnet, it ismade part; of aclosed magnetic circuit and astrongr magnetomotive force applied. `When the appliedmagnetomotive force is reduced Yto zero, the induction does not return to zero. Its value is. the vertical intercept ofthe usual hystersis loop represented` by V@win Fig. 5. l

llVhen` the magnet Ais removed from the closed magnetic circuit, the poles exert a demagnetizing effect. This may be regarded as a negative magnetomotlive force and so is represented in F ig. 5 by the abscissee H, which are measured toward the left. The problem is to so choose the length and cross section of the permanent magnet that this de-magnetizing effect of the poles is of the most advantageous size.

The only magnetomotive force in th magnetic circuit, after the magnetizing process is over, is that of the poles. This must, therefore, not only reduce the induction Withinthe permanent magnet from 0a to itsinal value,ksay bc, but itmust also cause the fluir through the air gaps 5, 7 and|8 and the diaphragm. The magnitude of the lluxthrough these air gaps being decided upon, the required magnetomolive force is fixed.

Neglecting the eliect of leakage through the sides of the permanent magnet We may write MzI-Il, Where M is the magnetoinotive force in Gilberts, H is the cle-magnetizing effect of the poles in Gilberts per centimeter and 1 is the length in centimeters.

If'A be the area of cross section of the magnet and v its volume, We have M v-Al -A H and, representing the induction by B and the fiux by 1, We may multiply both terms ofthe fraction by B and obtain rlhe magnetomotivc force M and the flux E being .fixed by the required conditions in the air gaps, this equation showsI that the volume will be a. minimum when BH is a maximum.

rlhe curve Il in Fig. 5 shows how the product BH changes with different values of B. It Will be apparent, from inspection thereof, that the maxinnnn value of the product occurs near the point (l, for which BIGOOO.

Therefore, dividing the flux 1) by (S000 gives the most desirable area of cross seetion. The length is then found by dividing the volume, determined by considerations sta-ted above, by the cross section;

A numerical example is inserted to malte the foregoing discussion concrete. In a receiver of the type illustrated in Fig. l, the fiux in the air gap 7 should be about 2500 Biaxivells. The reluctance of the magnetic circuit, through the permanent magnet and the diaphragm is ordinarily such that a magnetomotive force of 180 Gilbertsis required to produce the 300 Maxivells ofr [lux therein.

The flux (I) in the magnet must supply not only these SOO-B'la-Xu'ells but also the ll'nx through the shunt path including the air gap This is some live times as great.

The total flux. in the permanent magnet is,

therefore, 1800 Maxwells The product of the linx (D by the magnetomotive force M is, therefore, 1800 180: 824,000. lf thisbe divided by BH we shall obtain the volume. The induction B must be about (S000, because curve ,lil shon's a maximum at that ordinate. The value of H corresponding to B:G000 is shown by curve I to be 158. The product BH is, therefore, G00O 153:91S.000. Dividing 321,000 by 918,000 gives the volume of the magnet as 0.353 cubic centimeters.

The flux, 1800 Maxwells, when associated with an induction of 6000 Gausses, gives lll) fi t

`tion l gives the length, 0.353+G.3:1.l77.

Again, the magnetomotive torce, 180 Grilberts, being associated with `1.53 Gilberts per centimeter for the valueo't H, we have 180+ 153:1.176 `centimeters tor the length of the.

magnet which agrees with the length as determined above.

The surprisingly small values for the volume and length ot' the magnet are a consequence of two considerations; tirst, a material is selected tor which the product BH is greater than for other materials, and then a shape of magnet is selected which corresponds to the maximum value ot' the product BH. This will be evident from the curves in Fig. 5, where I and ll' represent the relation between the quantities BH, H, and B for a steel containing some 38% et cobalt, while the curves l and Il represent these relations for a steel containing 2% ot chromium. By selecting the cobalt steel and that value of B corresponding to the point l on the curve H, the resulting vohnne and length of the magnet are most advantageous.

The values of H represented by 06 for the chromium steel and by of tor the cobalt steel are the coercive forces ior these two materials. lt will be noticed that the steel having the greater coercive torce the one which also has the greatest maximum value for the product BH. It a choice were being made between two materials having nearly the same coercive torce, it might be that the maximum value et the product BH occurred in the material with the smaller coercive torce. It such circumstances should arise, the steel to be selected is the one lor which the product BH is largest, but ordinarily this is the one with the great est coercive torce.

The dimensions indicated` by the foregoing discussion are not strictly followed. There is some leakage through the sides ot the permanent magnet and, to allow lor this the volume must be slightly greater. Also the theoretical. length is a little greater than the distance between pole pieces in a telephone receiver ot standard size and the convenience ot manufacture, resulting trom following standardized dimensions, has caused a trifie shorter length to be adopted, although a volume somewhat greater than the theoretical. magnitude must then be used.

The above theoretical discussion describes the removal ot' the permanent magnet from the closed n'iagnetic circuit in which it was inagnetized. ln practice, the magnet 1 is magnetized in a closed magnetic circuit of which the pole pieces 2 and 3 :torni a part and the permanent magnet is lett in contact with the pole pieces at all times, after the original magnetination. It it were removed from them. the de-magnetizing ell'cct ot the poles would bring 'the induction `down to some such point as g (Fig. 5).

placing the magnet between the pole pieces, the induction would increase, not to the `value c as desired, but to some value such asili., which too small. y

The magnetic circuit through air gapsi, 'T and S, in series,l provides a path il'or the varying linx produced by the coils 12 and 14e which does not extend through the permanent magnet l. Consequently, the small response oit the material o'li the magnet l to the liuctuations in magnetomotive torce, does not cause any diminution et the changes which result from the changing current in the coils.

Although I have shown only one embodiment ot my invention in the accompanying drawing, it is capable ot various changes and modilications without departing from the spirit thereof and it is desired, theretore, that only such limitations shall be imposed thereon as are indicated in the prior art or in the appended claims.

I claim as my invention:

l. A telephone receiver device, comprising a diaphragm and a magnetic circuit, including pole pieces, air gaps, said diaphragm and a permanent magnet, the length of said permanent magnet being no greater than the distance between portions oi? said pole pieces adjacent said diaphragm.

2. A telephone receiver device, comprising a diaphragm and a magnetic circuit, including pole pieces, air gaps, said diaphragm and a permanent magnet, the volume of said per manent magnet being sutlicient to provide i'lux across the air gaps, of the magnitude needed to properly work the diaphragm, and

the cross section ot the permanent maglietbeing such that the magnetic induction therein has such a value that the said iuX is obtained in a length no greater than that bctween the portions of said pole pieces adjacent said diaphragm.

A telephone receiver device comprising in combination a diaphragm, pole pieces cooperating therewith, positioned nearer the center oi said diaphragm than ont-halt the radius thereot,A coils co-operating with said pole pieces and supplied with fluctuating current, a permanent steel magnet ot highcoercive-torce and of a length substantially equal to the separation ot said pole pieces adjacent the diaphragm, and a container case cooperating therewith.

4t. A magnetic circuit 'tor a telephone receiver, including a diaphragm, pole pieces cooperating with the diaphragm to form an approximately rectangular magnetic circuit, and a permanent magnet within the rectangle and constituting part ot the magnetic circuit.

nen, upon i5. A magnetic circuit for n telephone receiver, including@ diaphragm,- pole pieces cooperntingv with the daphvagm to form an approxinmtely rectangular magnetic circuit j andi :11 permanent magnet crossmg the 1n- .terolz of` the rectangle the shorter Wayl Y Wholly Within4 the rectangle, and Constitutother, L coil on the other arm of enchpole piece, :r dnphrngn'l adjacent to the ends of said last-named arms n. permanent magnet' barallel toA Said' fir/st named arms and a nonmagnetic spacing block betweensnd n'lagnet and said first-named arms.

In testimony whereof. I have hereunto subscribed my name this 22nd day ol' August 1924.

CLINTONv R. HANNA. 

